Over medium heat melt margarine or butter. Add potato water and milk, heat to 110°-115°F and set aside.

Mash potatoes to make 1 cup. Place the mashed potatoes and potato water mixture in a large bowl. Add the sugar, salt and eggs. Beat with a wire whisk until smooth. Stir in Yeast over all and beat again.

Add 2 cups of bread flour and beat until smooth. Mix in 3½ more cups of bread flour with a wooden spoon. Gradually add the last cup of bread flour, working it with your hands by pressing flour into dough and turning dough over until it is firm. Cover; let rise until dough tests ripe.

Punch dough down and place on a floured surface. Sprinkle dough lightly with flour. Press dough out with fingers to a square 1-inch thick. Cut in 1½ -inch wide strips lengthwise and equal width crosswise. If the knife gets sticky while cutting, just dust it with flour.

Shape each piece into a ball by pinching all four sides underneath to seal. Place buns almost touching in greased cake pans. Let rise covered until indentation remains after touching.

Bake in a preheated 400°F oven for 15 to 20 minutes. Cool on wire racks.

Hi Kim,
Yes, that should be fine to sub in buttermilk. We also have a few rolls recipes that specifically call for buttermilk. Here’s a link to one of them (one of our most popular recipes!) >> https://redstaryeast.com/buttermilk-pan-rolls/.
Happy baking!
Carol